The invention relates to monitoring the operational performance of fluid storage systems.
Large quantities of liquids and similar materials are often stored in bulk storage containers or tanks, which may be located above-ground, partially above-ground, or completely below ground. Such containers or tanks are generally connected by piping to flow-meters or dispensers.
For example, underground storage tanks (UST""s) and, occasionally, above-ground storage tanks (AST""s) are used to store petroleum products and fuel to be dispensed at automobile service stations, trucking terminals, automobile rental outlets, and similar operations through gasoline, diesel, or kerosene dispensing pumps. Fuel product is generally delivered to such facilities by a gravity drop from a compartment in a wheeled transport means such as a fuel delivery truck. AST""s or UST""s are often located at central distribution locations so that product can be subsequently withdrawn from the tank system to be transported for delivery to a variety of such facilities. A distribution location with UST""s or AST""s may receive deliveries of product from, e.g., a pipeline spur, wheeled transport, a barge, or a rail car.
Direct observation of the operating condition of such tanks and storage containers is difficult or impossible. The various methods for identifying the amount of product in tank systems have varying levels of accuracy, repeatability, and performance. Moreover, the accuracy of devices which measure the amount of product dispensed from the storage containers and tanks differs greatly, and may or may not be temperature compensated. The amount of product actually delivered to the tank system is often measured inaccurately and, frequently, not at all. Rather, the owner or operator of the tank or vessel usually records the invoiced amount of product delivered as the actual amount introduced to the tank system, without having any means of confirming whether the invoiced amount of product delivered is correct.
Consequently, effective management of such facilities is complicated by the numerous errors in the various measuring devices and procedures used to establish a baseline for management, planning and decisionmaking. Effective management requires the following:
1. Accurate measurement of the volume stored in the system.
2. Accurate determination of the volume dispensed from the system.
3. Accurate determination of the amount of product introduced into the system.
4. Identification of volumes added to or removed from the tank system which are not otherwise recorded.
5. Rapid identification of leakage from the tank system.
6. Continuous monitoring and diagnosis of the operating performance of all of the component measuring devices of the system.
7. Continuous analysis of sales data to predict demands of product from the system.
8. Determination of optimal reorder times and quantities as a function of ordering, transportation, holding, and penalty costs in order to minimize total costs of operation and/or to maximize profits.
Traditionally, these functions were performed crudely or, in many cases, not at all. Volume measurements were, and in many instances still are, based on imperfect knowledge of the geometry, dimensions, and configuration of the storage vessel. Also, dispensing meters are frequently miscalibrated. This is true even when tank systems are regulated, due to the breadth of tolerance permitted for individual sales as related to total tank volume. For example, deliveries from the delivery vehicle are almost always unmetered, additions of product from defueling vehicles are typically undocumented, and theft of the product is not uncommon.
Leakage of product has, in recent years, assumed a dimension far in excess of the mere loss of the product. Environmental damage can, and frequently does, expose the operator to very large liabilities from third party litigation in addition to U.S. Environmental Protection Agency (EPA)-mandated remediation which can cost in the range of hundreds of thousands of dollars. The EPA""s requirements for leak detection are set forth in EPA Pub. No. 510-K-95-003, Straight Talk On Tanks: Leak Detection Methods For Petroleum Underground Storage Tanks and Piping (July 1991), which is incorporated herein by reference.
To address these concerns, Statistical Inventory Reconciliation (SIR) was developed. The SIR method consists of a computer-based procedure which identifies all of the sources of error noted above by statistical analysis of the various and unique patterns that are introduced into the inventory data and, in particular, into the cumulative variances in the data when viewed as functions of product height, sales volumes, and time.
The present invention relates to an automatic SIR system that may continuously and automatically collect data from completely above-ground, partially above-ground, and completely below ground containers for statistical analysis. The invention addresses a variety of physical, business, operational and environmental issues associated with the bulk storage of liquids or pourable solids.
The present invention is an application of SIR that greatly enhances the ability to manage a facility effectively. It provides the means to characterize exactly the geometry, dimensions, and configuration of the storage vessel, identify overages and shortages in deliveries and unexplained additions and removals of product, and provide an accurate assessment of overall dispensing meter calibration. In addition, by accounting for such discrepancies, the present invention permits identification of leakage at rates less than 0.1 gallon per hour in all of its estimates to any prescribed tolerance. By increasing the number of measurements taken, the estimates can be derived at any desired level of tolerance.
The method of the present invention makes no assumptions as to the precision of any of the measuring devices used in various system configurations. Precision and calibration accuracies are derived from the data alone. Also, it is not assumed that the tank system is leak free; the leak status of the system is determined from the data alone.
The method derives tank geometry, dimensions, and configuration, and their impact on the totality of cumulative inventory variances, as a function of product height in the tank. Correctness of dispensing meter calibration is verified in a similar manner by testing for randomness of cumulative variances as a function of varying sales volumes. Having confirmed that such remaining residual variances are random, reflecting only the inherent random noise of the measurement devices, the present method analyzes departures of the cumulative variance from the bounds determined by the calculated random noise level. All calculations as to the volumes added, removed, metered or leaking are based upon extended successive, simultaneous observations of meter and gauge readings. The number of observations incorporated in each such calculation is determined by computing confidence bands for the parameters of interest and extending data collection as necessary to achieve predetermined tolerances.
For example, the method of the present invention is capable of distinguishing between continuous losses consistent with leakage and one-time unexplained removals of the fluid product from the tank. The method may be used to ensure the accuracy of computed delivery volumes, which are determined and reported with confidence boundaries calculated for estimated delivered quantities.
The method can also be used to control and monitor the accuracy of purchase costs of fluids such as petroleum which are delivered to tanks. For example, motor fuel retailers may be charged by wholesalers for either net or gross volumes purported to have been delivered. A determination that purchase charges are appropriate thus requires frequent simultaneous readings of sales, tank volumes and temperatures, which can be accomplished using the method of the present invention.
To accomplish these goals, the present invention involves estimating changes in product volume in a tank based on multiple data points and their respective likely errors measured continuously over a period of time. A software program is used to implement an algorithm that employs concepts from matrix theory and mathematical statistics. The algorithm includes generating the product of a matrix and its transpose by successive additions of partial products of partitions of the matrix and their corresponding transposed matrix partitions to minimize the storage requirements of the data collected. The compressed matrix data constitutes a complete and sufficient statistic for the parameters of interest. The algorithm thus permits the accumulation and storage of a large amount of data in a condensed form without sacrificing statistically useful information, to obtain a statistically significant result with the required accuracy and reliability.
In general, in one aspect, the invention features a method of monitoring a fluid storage and dispensing system, the system including measurement apparatus for measuring a volume of fluid associated with the system and a plurality of temperature sensing devices disposed at a plurality of locations within the system. A plurality of measurement data are collected from the measurement apparatus and the plurality of temperature sensing devices in a form readable by a computer. The plurality of measurement data are stored in a compressed matrix format in a computer memory. The compressed matrix format is statistically analyzed to determine operational monitoring information and to calculate the volume of fluid based on the measurement data collected from the measurement apparatus and the plurality of temperature sensing devices.
Implementations of the invention may include one or more of the following features. The statistically analyzing step may include determining a correction value for the calculated volume based on a weighted average of the temperature of the fluid simultaneously measured at the plurality of locations within the system.
The method may include determining the presence of operational defects in the system based on the operational monitoring information. The method may include monitoring the accuracy of the measurement apparatus and the plurality of temperature sensing devices based on the operational monitoring information.
The method may include determining whether a quantity of fluid removed from the system is caused by a leak in the system based on the operational monitoring information. The method may include delivering a warning if a leak is determined to exist in the system.
The collecting step may be performed continuously at periodic intervals. The method may include querying the measurement apparatus and the plurality of temperature sensing devices under the control of the computer.
The storing step may include generating the compressed matrix format as a product of a data matrix and the transpose of the data matrix. The product may be formed by addition of partial products of each of a plurality of partitions of the data matrix with the transpose of each partition.
The method may include transmitting the measurement data to a host processor to perform the statistically analyzing step. The method may include transmitting the compressed matrix format to a host computer to perform the statistically analyzing step.
In general, in another aspect, the invention features a method of monitoring a fluid storage and dispensing system, the system including a plurality of measurement apparatus for measuring a volume of fluid associated with the system. Measurement data from the plurality of measurement apparatus is simultaneously collected in a form readable by a computer to determine a change in the volume. The collecting step is repeated to obtain a plurality of the measurement data. The plurality of measurement data is stored in a compressed matrix format in a computer memory. The compressed matrix format is statistically analyzed to determine operational monitoring information.
Implementations of the invention may include the following feature. The method may include estimating an initial value of the volume during the statistically analyzing step based on the operational monitoring information.
In general, in another aspect, the invention features a method of monitoring a fluid storage and dispensing system, the system including measurement apparatus for measuring a volume of fluid associated with the system and a plurality of temperature sensing devices located at different heights in the system, the volume having a height in the system. A plurality of volume measurement data is collected from the measurement apparatus in a form readable by a computer. The volume measurement data is adjusted based on temperature measurements taken from those of the plurality of temperature sensing devices at a height below the height of the volume in the system. The plurality of volume measurement data is stored in a compressed matrix format in a computer memory. The compressed matrix format is statistically analyzed to determine operational monitoring information.
In general, in another aspect, the invention features a method of determining a volume of fluid associated with a fluid storage and dispensing system, the volume of fluid having a height in the system, the system including measurement apparatus for measuring the height. A plurality of height measurement data is collected from the measurement apparatus in a form readable by a computer. The plurality of height measurement data is stored in a compressed matrix format in a computer memory. Regression analysis is performed using the compressed matrix format to calculate the volume of fluid associated with the system.
Implementations of the invention may include the following feature. The collecting step may be performed each time a portion of the volume of fluid is dispensed from the system.
In general, in another aspect, the invention features an apparatus for determining a volume of fluid associated with a fluid storage and dispensing system, the volume of fluid having a height in the system. Measurement apparatus measures the height of the volume of fluid. A computer includes a processing means for collecting a plurality of height measurement data from the measurement apparatus and a memory for storing the plurality of height measurement data in a compressed matrix format. The processing means performs regression analysis on the compressed matrix format to determine the volume of fluid associated with the system.
In general, in another aspect, the invention features a method of determining a plurality of volumes of fluid, each of the volumes associated with one of a plurality of fluid storage and dispensing systems, each of the volumes having a height in its associated system, and each of the systems including measurement apparatus for measuring the height of each of the volumes of fluid. A plurality of height measurement data is collected from the measurement apparatus of each of the plurality of systems in a form readable by a computer. The plurality of height measurement data is stored in a compressed matrix format in a computer memory. Regression analysis is performed using the compressed matrix format to calculate the volumes of fluid associated with the systems.
In general, in another aspect, the invention features a method of monitoring a fluid storage and dispensing system including a tank for storing fluid and at least one measuring device for providing indications of status of the fluid. Data is collected from the at least one measuring device at a plurality of times, the collected data including data representative of a device-indicated volume of the fluid in the tank. An analytic tank fluid volume is calculated at each of the plurality of times. An expected volume difference between the analytic tank fluid volume and the device-indicated volume is calculated at each of the plurality of times. An actual volume difference between the analytic tank fluid volume and the device-indicated volume is calculated at each of the plurality of times. An indication of a pattern of the relationship between the expected volume difference and the actual volume difference at the plurality of times is provided.
Implementations of the invention may include one or more of the following features. The relationship between the expected volume difference and the actual volume difference may have a nonrandom pattern indicative of a loss of fluid from the tank. The collecting step may include collecting data indicative of a level of the fluid in the tank and the analytic tank fluid volume is a function of the level of the fluid in the tank. The expected volume difference calculating step may include calculating an expected analytic volume based on at least one tolerance value of the at least one measuring device.
The collecting step may include providing computer readable data indicative of amounts of fluid delivered to the tank, amounts of fluid removed from the tank, and levels of fluid in the tank, the method further including storing the computer readable data in a compressed matrix format in a computer memory, the compressed matrix being a product of a data matrix of the computer readable data and a transpose of the data matrix. The storing step may include adding partial products of each of a plurality of partitions of the data matrix with the transpose of each partition. The collecting step may provide data indicative of cumulative fluid delivery to the tank and removal from the tank.
The method may include estimating a differential of a volume function of the volume of the fluid, the volume function being a function of the level of the fluid in the tank, and integrating the differential of the volume function to yield the volume function, such that the step of calculating analytic tank fluid volume includes evaluating the volume function for a desired fluid level.
The collecting step may include collecting data indicative of the temperature of the fluid at each of the plurality of times and the step of calculating the analytic tank fluid volume may incorporate the temperature data.
The method may include determining whether fluid is leaking from the tank based on the indication of the pattern of the relationship between the expected volume difference and the actual volume difference. The providing step may provide an indication that fluid is leaking from the tank.
In general, in another aspect, the invention features a fluid storage and dispensing system including a tank for storing the fluid. A plurality of measuring devices provide, at a plurality of times, data indicative of fluid status including data representative of a device-indicated volume of the fluid in the tank. A processor receives the data from the measuring devices, calculates an analytic tank fluid volume at each of the plurality of times, calculates an expected volume difference between the analytic tank fluid volume and the device-indicated volume at each of the plurality of times, calculates an actual volume difference between the analytic tank fluid volume and the device-indicated volume at each of the plurality of times, and provides an indication of a pattern of the relationship between the expected volume difference and the actual volume difference at the plurality of times.
Implementations of the invention may include one or more of the following features. The relationship between the expected volume difference and the actual volume difference may have a nonrandom pattern indicative of a loss of fluid from the tank. The processor may reduce the amount of received data by storing the data in a compressed data matrix format, the compressed data matrix being a product of a data matrix and a transpose of the data matrix.
The measuring devices may include a volume level indicator and a dispensing apparatus. The volume level indicator may include a magnetostrictive tank probe. The dispensing apparatus may include a totalizer.
The system may include a leak indicator coupled to the processor for providing a leak indication if the relationship between the actual volume variance and the expected variance has a continuously nonrandom pattern. The system may include a one-time volume change indicator coupled to the processor for providing an indication of a one-time volume change if the processor determines that the difference between the actual volume difference and the expected volume difference exceeds a predetermined amount.
In general, in another aspect, the invention features a computer program product residing on a computer readable medium for use with a fluid storage and dispensing system including a fluid storage tank and at least one status device for providing indications of fluid status. The computer program product includes instructions for causing a computer to receive at least a portion of the indications of fluid status at a plurality of times and determine a computed tank fluid volume, receive the portion of the indications of fluid status at each of the plurality of times and determine a measured tank fluid volume as indicated by the at least one measuring device, determine an expected volume variance between the computed tank fluid volume and the measured tank fluid volume, determine an actual volume variance between the computed tank fluid volume and the measured tank fluid volume, and determine a pattern in the relationship between the actual volume variance and the expected volume variance.
Implementations of the invention may include one or more of the following features. The instructions for causing the computer to determine a pattern in the relationship between the actual volume variance and the expected volume variance may cause the computer to determine a nonrandom pattern indicative of a loss of fluid from the tank. The instructions for causing the computer to determine a pattern may further cause the computer to provide a leak indication if the relationship between the actual volume variance and the expected variance has a continuously nonrandom pattern.
The indications of fluid status may be stored as data, and the computer program product may include instructions for causing the computer to reduce the amount of data stored. The instructions for causing the computer to reduce the amount of data stored may cause the computer to determine a product of a data matrix containing the data and a transpose of the data matrix. The instructions for causing the computer to reduce the amount of data stored may also cause the computer to determine the product by adding partial products of each of a plurality of partitions of the data matrix with the transpose of each partition.
The computer program product may include instructions for causing the computer to determine the tank fluid volume as a function of a level of the tank fluid using at least a portion of the indications of fluid status. The instructions for causing the computer to determine the tank fluid volume may cause the computer to determine coefficients of a polynomial. The instructions for causing the computer to determine the tank fluid volume may cause the computer to estimate a differential of the volume function and integrate the estimated differential to determine the tank fluid volume.
The computer program product may include instructions for causing the computer to provide an indication that the actual volume variance and the expected volume variance differ by more than a predetermined amount.
An advantage of the present invention that the accuracy and consistency of devices used to measure volume of product added to, removed from, and present in a fluid storage system may be determined.
Another advantage of the present invention is that additions of material to the system, but not recorded as such, and volumes of product removed from the system which are not registered by measuring devices or otherwise recorded, may be identified.
Another advantage of the present invention is that discrete one-time unrecorded removals of product from the system may be distinguished from continuous losses consistent with leakage.
Another advantage of the present invention is that product leakage from all parts of the system, extending from the fill point to the point of discharge, may be identified and confirmed.
Another advantage of the present invention is that secular, seasonal trends and repetitive special demands to provide short and long term estimates for demand of the product, and optimal reorder quantities and delivery schedules, may be identified and determined.
Another advantage of the present invention is that a better estimation of product volumes and volume changes may be obtained by calculating the differential of the volume function.
A further advantage of the present invention is that all of the foregoing may be accomplished in a fully automated system that requires no human intervention, other than as an option available to the operator to enter quantities of material reportedly delivered for comparison with those computed.
Other features and advantages of the invention will become apparent from the following detailed description, and from the claims.